Transposition of insulating core windings

ABSTRACT

A device for reducing the incidence of circulating currents within the coil structure of multiple-conductor windings of transformer/reactors of the insulating magnetic core type, by a transposition of the electrical connections between the several conductors of the multiple-conductor winding at the outer part of the winding after the core and coil assembly is completed. When effecting the necessary electrical connections between adjacent outer layers of winding, connections between analogous conductors of the multiple-conductor bundle are interchanged, the outermost conductor of one bundle being connected to the innermost conductor of the other bundle, second-outermost conductor of the one bundle being connected to the second-innermost conductor of the other bundle, and so forth.

United States Patent [191 Johnson 1 51 May 1, 1973 [54] TRANSPOSITION OFINSULATING [73] Assignee: High Voltage Power Corporation,

Westboro, Mass.

22 Filed: July 3,1972 21 Appl. Na; 268,761

[52] US. Cl. ..336/l87, 336/212, 336/219 [51] Int. Cl. ..H01f 27/28 [58]Field of Search ..336/69, 70, 180,

[56] References Cited UNITED STATES PATENTS Primary Examiner-Thomas J.Kozma Att0rneyHenry C. Nields [57] ABSTRACT A device for reducing theincidence of circulating currents within the coil structure ofmultiple-conductor windings of transformer/reactors of the insulatingmagnetic core type, by a transposition of the electrical connectionsbetween the several conductors of the multiple-conductor winding at theouter part of the winding after the core and coil assembly is completed.When effecting the necessary electrical connections between adjacentouter layers of winding, connections between analogous conductors of themultiple-conductor bundle are interchanged, the outermost conductor ofone bundle being connected to the innermost conductor of the otherbundle, second-outermost conductor of the one bundle being connected tothe second-innermost conductor of the other bundle, and so forth.

PATENTEDHAY 1 1915 SHEET 1 OF 2 TRANSPOSITION OF INSULATING COREWINDINGS BACKGROUND OF THE INVENTION This invention relates tohigh-voltage insulating core type electrical induction apparatus andmore particularly to a device for reducing power loss in such apparatusby employing multiple conductor bundle windings but avoiding difficultinternal transpositions.

Today, the pressing requirement for more and cheaper electrical powerfaces growing technical and esthetic problems including the nationaldesire to maintain the attractiveness of populated areas. To meet thiscontinuing need for more electric power without adding more generatingand transmission systems within cities and surburban areas, electricutilities are now building power plants in remote regions close to thesource of either large amounts of hydropower or large coal deposits.This power can be transmitted to load centers most economically byoverhead transmission lines. However, because of increased populationdensity and pressure to preserve the esthetic and economic values of thecountryside, transmission rights-of-way are increasingly difficult toobtain. The utilities are thus compelled to increase several-fold thepower transmitting capacity of their existing right of ways, and to planon still further increases in power in the future. Forthese and otherreasons, the electric power industry is rapidly converting to extra highvoltage (El-IV) for the transmission of electric power havingline-toline voltages in excess of 345 KV. Already 500 KV systems are inservice, and more recently 765 KV systems have been energized. Such highvoltages permit the transfer of larger blocks of power over extensivegeographic areas. EHV interconnections are also used to even out demandsover large regions and to improve the reliability of the total system.Indeed, the trend toward higher voltages is fundamental to meeting thepredictable power needs of the next decade.

As electrical devices have developed, different techniques have evolveddepending upon the magnitude of the various parameters involved. Forexample, high voltage d.c. equipment entails strong electric fields andhigh power a-c equipment has come to entail strong magnetic fields.Specialized techniques have been worked out for handling these strongelectric fields in high voltage d.c. equipment: for example, megavoltaccelerator apparatus employ hollow, rounded high voltage terminals andequipotential planes for controlling the electric field and shaping ituniformly. On the other hand, different specialized techniques have beenworked out for handling the strong magnetic fields of high power a.c.equipment: for example, ferromagnetic material is used to form magneticcircuits in which elaborate steps are taken to minimize reluctance andeddy currents. However, the need for these specialized techniques existsonly for certain ranges of certain parameters. For example, conventionalhousehold appliances do not require special techniques for shapingelectric fields, and high-voltage electrostatic accelerators do notrequire ferromagnetic material.

Conventional electric power techniques have evolved in a similar manner.Initial efforts involved d.c. and the requirements of average householdequipment, such as lighting, led to voltages of the order of volts.

With the development of a.c. and transmission of electric power overgreater distances at higher voltages to reduce losses in transmission,apparatus capable of handling voltages of the order of 10 volts weredeveloped, and related insulating and magnetic circuit techniques weredevised. Such techniques were limited to their own range, however, andthe more recent interest in even higher voltages for power transmissionhas triggered a need for fundamentally new approaches and has generatednew generic names: EHV (which stands for extra high voltage and includesthe range 345-765 kilovolts in overhead systems and 230 kilovolts and upin underground systems) and UHV (which stands for ultra-high voltage andincludes the voltages above 765 kilovolts now contemplated for overheadtransmission). At the extra-high voltage range, problems not beforefaced must be solved: the Ferranti effect becomes a problem intransmission lines, the strong magnetic fields required by transformersmust overlap the strong electric fields which must be controlled atthese high voltages, and other new problems arise.

The basic approach to the design of apparatus for coping with strongelectric and magnetic fields is disclosed in the insulating-core patentsof Van de Graaff, and more recently of Trump, et al. US. Pat. No.3,684,991. The present invention is an improvement and refinement ofthese approaches in which insulating-core principles are applied toelectromagnetic induction apparatus for use with EHV and UI-IVtransmission lines for the absorption and storage of large quantities ofelectric charge associated with the capacitance of long transmissionlines, or in the transfer of power from one voltage level to another insuch large megavoltampere amounts.

Due in part to the insulating gapsin the magnetic core of such devices,a significant magnetic field frequently exists in the coil structure,beyond the physical boundaries of the core. Changes in the magneticfield may thus induce eddy currents in the coil conductors resulting ininefficiencies from losses in the form of heat and of attendantdeterioration of insulation and reduction of life of the device.

Since eddy current loss decreases relatively quickly when conductorthickness is decreased in the dimension transverse to that of themagnetic field, it is possible, subject to practical limitations, toreduce eddy current incidence by subdividing the conductor in thedimension extending radially from the axis of the magnetic field, sothat the conductor thickness in this radial dimension is relativelysmall. In order to preserve current-handling capability of the windingin high-power apparatus, one must preserve or even increase thedimension of the conductor in the dimension parallel to that of themagnetic field. Accordingly, reducing eddy currents in high-powerapparatus may result in a winding which has a plurality of lengths ofconductive tape. In insulating-core apparatus of this type, the innerextremity of each tape is connected to a ferromagnetic core element, andthe tape is spirally wound in a layer about said core element. Dependingupon the extent of subdivision of the conductor to reduce eddy currents,two or more such tapes in each spiral layer are connected in parallel.

Because the insulating core construction requires the connection of eachtape to the core at the tapes inner extremity, the conductor-subdivisionrequired for eddy current reduction results in parallel paths betweensuch connections. I have discovered that circulating currents resultingin substantial power loss occur in the closed paths formed by suchparallel paths unless special precautions are taken, in accordance withthe invention, to insure that the electromotive force generated abouteach such closed path is minimized.

In accordance with the invention, the outer extremities of such tapesare not connected to each other, and in making the necessary connectionsbetween adjacent spiral layers, the outer extremity of each tape isconnected only to the outer extremity of that adjacent tape which willminimize the electromotive force around the loops formed by the parallelpaths between the inner extremities of the two tapes thus connected attheir outer extremities. In other words, the electromotive forcegenerated between the inner extremities of each thus-connected pair oftapes in a pair of adjacent spiral layers is substantially the same forall such tape-pairs.

More specifically, in insulating core type transformer/reactors it maybe desirable to utilize a winding of n individual conductors. Anindividual conductor may be a conductive tape or band, and a conductorbundle may be n such tapes juxtaposed in front-to-back insulatedrelation and spirally wound about a core element to form substantially adisc-shaped coil section. At the inside of each coil section, all theconductors of the coil are electrically connected to the associated coreelement. To minimize circulating currents, it is important that theelectromotive force in all conductors between adjacent core connectionloci be substantially identical. However, in any turn of the spiralcoil, the n conductors of a bundle each follow different paths withrespect to the magnetic flux surrounding the core. As the spatialrelation of the conductors to each other remains constant from turn toturn of the spiral section, this path-flux discrepancy between thevarious conductors of the bundle is augmented with every turn of thecoil.

At any point along the length of the wound conductor bundle, theindividual conductors may be related by their distances from that pointto the core element (measured along a line through and perpendicular tothe longitudinal core axis). One conductor will be closest to the core,one farthest, and others intermediate distances. If this measurement isperformed at another location along the length of a wound bundle, thesame conductor will be found to be closest (farthest) to the core as wasdetermined in the first measurement, and,in general, the i'" closestconductor of the bundle at one location is the i" closest conductor atany location. This ordering relation of course cor" responds to theorder in which the conductors are juxtaposed in front-to-backrelationship when being spirally wound. Therefore, the conductors of thebundle may unambiguously be designated by terminology such as innermost,outermost, second-innermost, etc.

It will readily be recognized in such an arrangement that, at anylocation along the spirally wound conductor bundle, any two individualconductors are related also in the following ways:

1. The inner conductor has a greater instantaneous curvature than theouter conductor,

2. The length of the inner conductor from the core to the selectedbundle location is less than the corresponding length of the outerconductor,

3. The inner conductor couples fewer lines of magnetic flux than doesthe outer conductor. Therefore, the flux-induced electromotive forcewill differ between these two conductors, thereby contributing to an EMFdiscrepancy between parallel conductive pathways between adjacent coreconnection loci.

The present invention provides a construction and transposition whichwill tend to reduce the flux-induced EMF discrepancies among theindividual conductors of the multiple conductor winding, minimize eddyand circulating current incidence and resultant power loss and thermaldeterioration of insulation. While the efficiency of the invention willvary depending on the symmetries of the conductor-coil arrangements andthe magnetic field outside the core in the vicinity of the coils,excellent results are achieved with the spirally wound disc-like coilsections suggested above and described more fully below in connectionwith the preferred embodiments.

It is an important feature of the present invention that thetransposition involves only the outer edge of the winding. This permitstransposition after the assembly of the core and coil structure andallows the transposition to occur where magnetic flux is minimal ornear-zero. Due to the nature of insulating core type induction devices,internal transpositions are effected only with great difficulty.Additionally, the transposition of the present invention does not addsignificantlv to theexpense or size of the coil or winding structure,and there is no interference with the surge and distribution method ofthe transformer/reactor. The invention works effectively with two,three, four, or a larger number of individual conductors within thebundle.

SUMMARY OFTHE INVENTION Briefly, the present invention accomplishes theabove objectives by interchanging the electrical con-.

nections between individual conductors in windings of the aforementionedtype. Suchinterchange occurs at the points, on the outer layer ofwinding, where windings associated with adjacent core elements are to beelectrically connected. In particular, where a conductor bundle containsn individual conductors, ordered in the above-described sense, thei"'-outermost conductor of the bundle associated with one core elementis connected to the i"-innermost conductor of the bundle associated withthe adjacent core element, for values ofi=l ,2, n.

BRIEF DESCRWTION OF THE DRAWINGS FIG. 1 shows a diagrammatic view of areactor of the insulating core type.

FIG. 2 shows the manner in which coil sections are wound.

FIG. 3 shows an alternate manner of winding adjacent coil sectionsassociated with the same core element.

FIGS. 4, 5, 6 indicate possible coil configurations and the scheme ofelectrical connections between adjacent coil sections.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of thepresent invention may be seen in connection with FIG. 1, which shows aninsulating core type reactor useful in handling high voltages.

Here the magnetic circuit comprises a pair of end yokes 11 and 12 whichcouple a pair of segmented legs 13 and 14, each formed of a plurality ofsimilar, coaxially aligned core elements such as 15 and 15', withinsulating layers 18 separating the core elements.

Surrounding each core segment 15 is a coil winding comprising at leasttwo coil sections 16 and 17. All conductors of each sections areelectrically connected to their associated core segment, therebyestablishing the electric potential level of the core segment atsubstantially that of the coil. Taken in totality, the coils of each leg13, 14 provide multiple electric paths encircling the length of eachleg. The manner in which the coil sections are arranged and electricallyconnected to each other and to the leg segments is described in moreparticularity in connection with succeeding figures.

Here the high voltage lead 19 is located at the center of the legs.Other leads (not shown) are located near the ends of the legs or at theyokes.

FIG. 2 shows a portion of core element 15 from FIG. 1 and a portion ofits associated coil sections 16, 17. The coil section 16 is composed ofa spiral winding of a conductor bundle containing n individualconductors 16,, 16 16,, labelled in ascending subscript order from theinnermost (closest to the core) to the outermost (farthest from thecore).

Each conductor 16, through 16, is of the form of a tape or flexibleband. While the invention is not limited to conductors of this nature,it has been found that such conductors have convenient electrical andmechanical properties. A conductor bundle comprises the n individualconductors aligned in a front-to-back relation, adjacent conductorsbeing electrically separated by suitable insulating material.

FIG. 3 shows two coil sections 36 and 37, associated with the same coreelement 35, wound simultaneously as a single unit 31. Coil section 36consists of n conductors here labelled 36,, 36,, from innermost tooutermost in the manner described on connection with FIG. 2, above.Similarly, coil section 37 consists of n conductors 37,, 37,. Theadjacent coil sections 36 and 37 are electrically connected in parallel,as described below in connection with FIG. 6. Multiple coil sectionunits such as 31 may aid in enabling the electromagnetic apparatus tohandle high current requirements. In addition, where the magnetic fluxexternal to the core deviates from parallel to the core axis, adesirable electromotive force equalization may be achieved bysubdividing each tape conductor, such as 16,, l6, of FIG. 2, into aplurality of conductors each of which may be narrow in the dimension ofthe core axis as well as in the radial dimension. Such a subdivisioninto two parts is shown embodied in the twocoil section unit 31. Thenarrowing effect is suggested in the drawings in that the conductors ofcoils 36 and 37 of FIG. 3 are all narrower in the direction of the coreaxis than are the analogous conductors of coil 16 of FIG. 2. Inpractice, where the flux geometry makes such subdivisiondesirable,-greater subdivision, hence multiple coil section units withgreater numbers of coils, may be useful. Electrical connections may bemade in a fashion analogous to that indicated in FIG. 6. It is to beunderstood herein that multiple coil sections units may be employed inplace of two (or more) single coil sections where appropriate andconvenient.

FIG. 4 is a representation of a portion of the reactor of FIG. 1,illustrating details of a preferred coil configuration and electricalconnections of the present invention. Each coil section 16, 17, and 17'is formed from a spiral winding of a two-conductor (20 and 21) bundlesimilar to that of FIG. 2.

Coil sections 16 and 17, associated with the same core element 15, haveall conductors connected 22 at the inside of the coil sections, to eachother and to the core element.

Adjacent coil sections 16 and 17, associated with adjacent core elements15 and 15', respectively, are connected to each other at the outer partof the winding. In effecting the connection 23, the two conductors ofeach winding are transposed, the outer conductor of the winding of eachof coil sections 16 and 17' being connected to the inner conductor ofthe winding of the other coil section. An important feature of thepresent invention is that due to the convenient location of thetransposition, the connections may be carried out after otherwisecompleting assembly of the core and coil structure.

Coil section 17, adjacent to high voltage lead 19, has both conductorsof its winding connected to the high voltage lead at the outer part ofthe coil section.

FIG. 5 illustrates the transposition connection 24 where the coilsections 26 and 27 consist of an n conductor winding. As shown, the i"innermost conductor of the winding of one coil section is connected tothe (n+li),, innermost conductor of the winding of the other coilsection, for values of i=1 ,2,3, n.

FIG. 6 shows another possible coil arrangement which can be used inconnection with the present invention. Here each of the single coilsections 17, 17, 18 of FIG. 5 has been replaced by two similar coilsections 17a and 17b, 17'a and 17'b, 18a and 18b, respectively,connected in parallel. The transposition connection 25 is effected asillustrated by joining the outer conductors of coil sections 17 'a and17 'b to the inner conductors of coil sections 16a and 16b, and joiningthe outer conductors of coil sections 16a and 16b to the innerconductors of coil sections 17'a and 17'b.

It is to be understood that the foregoing discussion of the principlesand embodiments of the present invention is presented for descriptiveand illustrative purposes and not by way of limitation. The invention isnot limited to transformers or reactors, but also includes generatorswhich make use of insulating-core-type windings, such as the generatorsdisclosed and claimed in U. S. Pat. No. 3,239,702 to Van de Graaff.

Iclaim:

1. High voltage high power apparatus comprising a magnetic circuitincluding a series of alternating thick layers of ferromagnetic,electrically conducting material and thin layers of electricallyinsulating material,

a winding about said magnetic circuit having a plurality of spirallayers,

each spiral layer comprising a plurality of lengths of means connectingthe outer extremity of each tape to the outer extremity of a tape in anadjacent spiral layer,

said outer-extremity connecting means being such that the electromotiveforce generated between the inner extremities of each thus-connectedpair of tapes in a pair of adjacent spiral layers is substantially thesame for all such tape pairs.

2. Apparatus of claim 1 wherein each spiral layer comprises n conductivetapes, n 2, juxtaposed in front-to-back insulated relation and spirallywound to form substantially a disc about said one ferromagnetic layer.

3. Apparatus of claim 2 wherein said connections of outer extremities oftapes of adjacent spiral layers are such that the i"'-innermost tape ofone spiral layer is connected to the (n+1-i -innermost tape of the otherspiral layer, i-l,2, n.

4. Apparatus of claim 3 wherein 2 5 n 5 4.

5. Apparatus of claim 1 wherein about each said ferromagnetic layer arewound two units of spirallayers, each said unit comprising a pluralityof spiral spiral layers connected in parallel.

6. Apparatus of claim 1 wherein each said conductive tape is subdividedalong its width into a plurality of conductive parts connected inparallel.

1. High voltage high power apparatus comprising a magnetic circuitincluding a series of alternating thick layers of ferromagnetic,electrically conducting material and thin layers of electricallyinsulating material, a winding about said magnetic circuit having aplurality of spiral layers, each spiral layer comprising a plurality oflengths of conductive tape spirally wound about one of saidferromagnetic layers, each such length of tape being electricallyconnected at its inner extremity to said one ferromagnetic layer, aplurality of such lengths thus being electrically connected in parallelin order to handle high currents while preserving a small radialdimension so as to reduce eddy currents, means connecting the outerextremity of each tape to the outer extremity of a tape in an adjacentspiral layer, said outer-extremity connecting means being such that theelectromotive force generated between the inner extremities of eachthus-connected pair of tapes in a pair of adjacent spiral layers issubstantially the same for all such tape pairs.
 2. Apparatus of claim 1wherein each spiral layer comprises n conductive tapes, n > or = 2,juxtaposed in front-to-back insulated relation and spirally wound toform substantially a disc about said one ferromagnetic layer. 3.Apparatus of claim 2 wherein said connections of outer extremities oftapes of adjacent spiral layers are such that the ith-innermost tape ofone spiral layer is connected to the (n+1-i)th-innermost tape of theother spiral layer, i 1,2, . . . , n.
 4. Apparatus of claim 3 wherein 2< or = n < or =
 4. 5. Apparatus of claim 1 wherein about each saidferromagnetic layer are wound two units of spiral layers, each said unitcomprising a plurality of spiral spiral layers connected in parallel. 6.Apparatus of claim 1 wherein each said conductive tape is subdividedalong its width into a plurality of conductive parts connected inparallel.